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The premixed flame dynamics and pressure build-up in a closed duct with a 90° bend are experimentally and numerically investigated, and compared to a previous analytical theory. Emphasis is placed on the effect of the bend on the flame propagation, especially on the detailed flame front evolution. The results show that the finger flame is curved along the bend. A noticeable tulip flame is produced in the horizontal straight section as the upper parts of the indented flame nearly catches up with the lower parts. The lower parts tend to dominate the flame propagation after the complete formation of the tulip flame. The tulip flame disappears with the vanishing of the upper parts near the end of combustion. The flame dynamics in the experiment is reasonably reproduced by the numerical simulations, especially with isothermal wall. It is found that the full formation of the tulip flame is accompanied by a second drastic flame deceleration arising from the rapid reduction of the surface area of the outer flame front near the outer sidewall. It is revealed that the takes on the appearance of a “trough” shape after the flame touches the outer walls. The flame is still concaved from the center toward the burnt gas after the disappearance of the tulip upper parts. The pressure rise is closely related to the flame behavior. The heat transfer through the duct walls has a significant influence on the combustion dynamics. Both the flame tip location and pressure rise in the later stages are greater in the case of adiabatic duct walls than in the experiment. The theoretical analysis demonstrates that the flame propagation mechanism in the early stages in the curved duct coincides with that in a straight duct despite the presence of the bend. However, the flame behavior after its contact with the duct sidewall and tulip formation differs from those in a straight duct under the effects of the bend. [ABSTRACT FROM AUTHOR]

• Three kinds of 3D models with different units are proposed for a li-ion battery. • Thermal behavior is compared among the three models. • Several typical electrochemical properties are compared with the three models. • One unit model can replace the full-scale model for simplifying calculation. Recently, lithium-ion battery system appears to be an effective approach for energy storage due to their excellent performances. The internal structure of the lithium-ion pouch cell is laminated and is composed of several repeated units, and the unit includes five parts of positive current collector, positive electrode, separator, negative electrode and negative current collector. This structure brings great difficulties for simulator to develop full-scale model of the battery due to the complex calculation. In this paper, three kinds of three-dimensional layered electrochemical-thermal models with different unit numbers, one unit model (OUM), two unit model (TUM), and half-scale model (HSM) are established to study the effect of number of units on lithium-ion battery thermal behavior and electrochemical characteristics under adiabatic condition. The corresponding experimental procedure is performed for model validation, the simulation and experiment are in good agreement with temperature and discharge curves at four different discharge rates (0.5 C, 1 C, 1.5 C and 2 C). The results show that the temperature distribution and heat generation rate per volume as well as the representative electrochemical properties are almost the same of the three models; it is also found that each unit of the TUM and HSM is uniform and symmetrical distributed. Therefore, the HSM and full-scale model can be replaced by the OUM for lithium-ion pouch cell under adiabatic condition. The OUM can save 1/140 of computing time and greatly reduce the computational resources compared to HSM, which can facilitate the related research under adiabatic. [ABSTRACT FROM AUTHOR]

• The TR propagations of the large-format NCM and LFP modules are compared. • The critical parameters of TR propagation for both NCM and LFP modules are analyzed. • The toxicity of ejected gases from NCM module is greater than that of LFP module. LiNi x Co y Mn z O 2 (NCM) and LiFePO 4 (LFP) batteries are the two most widely employed in vehicles and energy storage stations, however, fire accidents related to them occurs frequently. A comparative analysis on the thermal runaway (TR) propagation behavior of NCM and LFP module are conducted in this work. Results indicate that intense jet fire and combustion behavior occurs in the NCM module, only a considerable amount of white smoke is observed in the LFP module. Generally, the duration time (t d) of TR and the maximum temperature (T max) of the NCM LIB are significantly higher than those of the LFP LIB. Compared with NCM modules, LFP modules are significantly less likely to suffer from TR propagation. Once TR propagation occurs in LFP module, the TR propagation in a single LFP LIB and LFP module is less aggressive and risk than in the NCM LIB and NCM module, respectively. And the TR propagation mechanism of the LFP and NCM modules are comparatively analyzed. Besides, the comparative analysis of gas production and gas toxicity of large format NCM and LFP module during TR propagation is revealed for the first time, which is very meaningful for the further evacuation and rescue of large-format LIB fires. It is found that the total mass of ejected combustible gases (including H 2 , CH 4 , C 2 H 4 , C 3 H 6 , CO) per failed cell number of the NCM module are much higher than that of the LFP module, which is determined to be 21.09 g and 4.17 g for the NCM and LFP module, respectively. Besides, the results calculated by the FED and FEC models demonstrate that the toxicity of ejected gases from NCM module is greater than that of the LFP module. This work present in detail the TR propagation characteristics of large-format NCM and LFP modules, which can provide valuable information for the safety design of lithium-ion batteries. [ABSTRACT FROM AUTHOR]

• The TR propagations of the large-format NCM and LFP modules are compared. • The critical parameters of TR propagation for both NCM and LFP modules are analyzed. • The toxicity of ejected gases from NCM module is greater than that of LFP module. LiNi x Co y Mn z O 2 (NCM) and LiFePO 4 (LFP) batteries are the two most widely employed in vehicles and energy storage stations, however, fire accidents related to them occurs frequently. A comparative analysis on the thermal runaway (TR) propagation behavior of NCM and LFP module are conducted in this work. Results indicate that intense jet fire and combustion behavior occurs in the NCM module, only a considerable amount of white smoke is observed in the LFP module. Generally, the duration time (t d) of TR and the maximum temperature (T max) of the NCM LIB are significantly higher than those of the LFP LIB. Compared with NCM modules, LFP modules are significantly less likely to suffer from TR propagation. Once TR propagation occurs in LFP module, the TR propagation in a single LFP LIB and LFP module is less aggressive and risk than in the NCM LIB and NCM module, respectively. And the TR propagation mechanism of the LFP and NCM modules are comparatively analyzed. Besides, the comparative analysis of gas production and gas toxicity of large format NCM and LFP module during TR propagation is revealed for the first time, which is very meaningful for the further evacuation and rescue of large-format LIB fires. It is found that the total mass of ejected combustible gases (including H 2 , CH 4 , C 2 H 4 , C 3 H 6 , CO) per failed cell number of the NCM module are much higher than that of the LFP module, which is determined to be 21.09 g and 4.17 g for the NCM and LFP module, respectively. Besides, the results calculated by the FED and FEC models demonstrate that the toxicity of ejected gases from NCM module is greater than that of the LFP module. This work present in detail the TR propagation characteristics of large-format NCM and LFP modules, which can provide valuable information for the safety design of lithium-ion batteries. [ABSTRACT FROM AUTHOR]